Optical discs, such as compact discs (CD) and digital versatile discs (DVD) are a form of computer readable media which provide extensive storage for digital information. One side of an optical disc may contain data and is referred to as a data side. The data side may be read only, or may also be written to. The other side of the optical disc that does not contain data may provide for a label and is referred to as the label side. In particular cases, a side or both sides may provide for data and a label.
An optical disc drive (ODD) of a computer may be used to read from and may write to a data side of an optical disc. An optical pickup unit (OPU), included within the optical disc drive, is configured with a laser and sensors adapted for reading, and possibly writing, data. Various ODDs and OPUs are available, and are manufactured to specifically read from and write to the data side of optical discs.
Using emerging technology, the OPU assembly may be used to produce an image on the label surface of an optical disc configured for such a labeling process. Producing the image includes positioning the OPU assembly at concentric circles of the optical disc where the image is written, and focusing an objective lens of a laser beam that performs the actual printing of the image on the optical disc. In certain embodiments, a material is applied to the label surface. The material reacts to create an image as the laser beam is applied.
Typically a voice coil motor (VCM) assembly carries the objective lens that focuses the laser beam used to label an optical disc. A VCM assembly may include one or more moveable VCM components such as metal coils which are activated by a voltage (or current) input that causes fine control movement of the objective lens in a particular direction. For example a moveable VCM component may cause the objective lens to move into and out of focus; another moveable VCM component may cause the objective lens to move to a track; and another moveable VCM component may cause the objective lens to tilt in an angular direction to the label surface.
The moveable VCM component that moves the objective lens in and out of focus is provided a voltage (or current) signal that moves the objective lens a predetermined distance. In order to move the objective lens the predetermined distance, calibration information defining how much movement is performed per amount of voltage (current) input applied to the moveable VCM component is utilized. For example, a moveable VCM component may be calibrated to move 1 micron per 1 mV applied. Therefore to move a 30 micron distance, 30 mV would be applied to (or removed from) the VCM component.
In some applications, the VCM component may also be affected by drift. Drift is defined as positional variances over time, operational usage, and temperature. For a particular VCM component, drift is the variation of movement or physical position for a given applied input voltage (current). In other words, although the voltage or current input applied to the particular moveable VCM component should cause it to move to a specific position, because of drift the actual resultant position may be different. Therefore the calibration of the moveable VCM component may change with drift. For example, instead of a 1 micron movement per 1 mV applied as per the example described above, drift may result in more or less than a 1 micron movement when 1 mV is applied.
Accordingly, there is a need for the present invention.